The objective is to study the mechanisms underlying the tactual discrimination of spatial form, excluding stereognosis, in the central nervous system of the primate. The plan includes psychophysical and neurophysiological experiments and the development of theoretical relationships between the two classes of results. I seek support in this application only for neurophysiological studies of the hand region of the primary somesthetic cortex of the primate. Psychophysical studies pertaining to the stimuli that will be used have already been completed as have neurophysiological studies of the responses of primary afferents (13, 48, 49, 82, 83, 84). These observations provide a background for the cortical experiments. The battery of stimuli used in the peripheral neurophysiological studies and in some of the psychophysical studies will be used in the cortical experiments. They are: (i) Braille-like dot patterns scanned across the skin; (ii) periodic mechanical gratings like those used in a psychophysical grating orientation task; and (iii) aperiodic gratings with a wide range of bar widths, gaps, and spatial frequencies. Assuming that neural responses in man and monkey are comparable, a set of neurons of the postcentral gyrus should show the capacity to resolve the Braille dot patterns and the mechanical gratings as effectively as do human subjects. Three main experiments are planned. (1) The Braille-like dot patterns will be used to study the response properties of neurons in the hand regions of areas 3a, 3b, 1 and 2. The aim is to identify, for further study, those neurons whose responses might provide the basis for fine form discrimination. (2) When the subregion containing neurons with highly structured responses to the Braille patterns and gratings is determined (current evidence suggests area 3b), that area will be studied intensively using the Braille dot patterns and periodic and aperiodic mechanical gratings. (3) The cross-species assumption and the role of attention will be studied.